Uml-based Gis Model Study

3D spatial data model is the core of 3D GIS. Modeling our world is difficult because of the massive data and complicated spatial relations in GIS. As a standard of modeling language, UML has abundant syntax and semanteme. UML is expressive and concise. It is a kind of modeling language with powerful functions that is suitable for the modeling complicated system.To solve the problem of massive data and complicated spatial relations in GIS, an idea of creating an object-oriented model based on UML is proposed. All the works can be dividing into several parts as follows:(1) UML can provide adaptive flexibility because user can define element of his own by the extension of mechanism. The stereotype extension mechanism can ensure stronger encapsulation and reusability. The tagged Value extension mechanism describes the detailed spatial relationship and the natural language accomplishes the constraint extension mechanism;(2) A method is adopted that integrate GRID with TIN because GRID is suitable for the flat terrain and TIN fit the precipitous land. Then DTM is established after modeling the ground object;(3) ROAM method based blocking partition is adopted to accomplish Multi-resolution terrain. The big binary tree of triangle is divided into small ones. Some blocks can be picked according to the view port. The rate of rendering moved up sharply by only rendering those necessary blocks;(4) OpenGL is used to render terrain and objects. Textures mapping, anti-aliasing, Blending, fog are applied to the fragments of terrain, and then the terrain is visualized. Furthermore, a portion of function is created.